Syncing (Genlocking) Arri Alexas from a Tentacle

As all the current Arri cameras (Alexa, Alexa Mini and Amira) can Genlock or sync from the timecode stream from a lock box, they can of course do so from a Tentacle. For long concert recordings where sync is important to prevent drift, I normally use another brand of lock box for this, and a client of mine is a bit worried about trying it with something so small as a Tentacle. We see a lot of Alexa Minis on hand held or steadicam rigs lately. The camera operators would prefer Tentacles!

I’d like to be able to tell him of people that are using Tentacles to Sync Arris in real life.Is anyone here doing this over longer takes (10min-90min) with success? The only post here I could find about this they were having trouble with green flashes, but I think their Tentacles were on the wrong framerate.

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Answers

many of our costumers do use Tentacles on ARRI Cameras, especially the ALEXA Mini, because its fits so good to the size of the camera 🙂

We have never tried this by ourself how long you can record a take and stay in sync without genlock. But I would say up to 30 minutes it is no problem when using ARRI products.

The other thing I would like to mention is that you can use Timecode as a Genlock Signal for Amira and Alexa Mini Cameras. This works great in general, but we have found out that these cameras do introduce a fixed offset wich is usually 1 frame (for SUP 4.xx).

Hi Ulrich, Thank you for the reply. I am aware of this, it is exactly how I work with Ambient Lockets on Arri cameras. I only bother where takes are longer than 10 minutes or so, but in my case filming concerts and Theatre, sometimes takes are 90 minutes long and drift is a real issue. What I was asking is if anyone has actually used or tested setting Genlock Sync to TC In using a Tentacle over long periods of time with success.

there is really no difference between Tentacle Sync and Ambient Lockits when connecting them via a 5pin LEMO to a camera. When the Genlock to TC-IN setting works with Ambient, it does work with Tentacle too. 5 Pin LEMOs do only carry timecode signal, there is no pin for Genlock inside the LEMO.

A way to find out the drift when not using genlock is to record also audio on the camera, preferably a duplicate of the separate audio recorder. Record a long take, for at least an hour. Then align the head of both camera audio and separate audio in ProTools sample accurate. Then look at the end how far they are apart.
Temperature may have an influence on this test but nowadays most clocks are good temperature compensated.